Various embodiments of antennas for reception of satellite broadcasted signals designed for mounting on vehicles have been studied and proposed. Since such an antenna is to be mounted, for example, on a roof or the like of an automotive vehicle running on a road where the height of the cars are legally restricted or, for example, on an aircraft where height is also an issue with respect to, for example, any drag associated with such an antenna that may result in decreased fuel efficiency, an important feature of such an antenna is to minimize a height of the antenna and an antenna mounting area. In addition, where the antenna is to receive at all possible times the satellite broadcasted signal and thus where the antenna at all times must be pointed in a direction of the satellite which will vary with time as the vehicle moves, it is important to have a tracking mechanism for controlling an azimuth and elevation angle of the antenna. However, the tracking mechanism can constitute a considerable part of the whole antenna manufacturing costs, complexity and height or mounting area of the antenna. Thus, it is important to minimize the space, complexity and requirements of the tracking mechanism and the antenna.
Disclosed, for example, in U.S. Pat. No. 5,579,019 (hereinafter the "'019 patent") is a slotted leaky waveguide array antenna for reception of satellite broadcast electromagnetic waves that may be mounted on a roof of an automobile. In particular, the '019 patent discloses a slotted leaky waveguide array antenna that enables reception of a direct broadcast satellite signal even with movement of the automobile, by providing an elevation beam width of about .+-.5.degree. in the elevation direction which is disclosed to be wide enough so that no tracking system need be used to move the antenna in the elevation direction. Thus the tracking mechanism and antenna of the '019 patent has an economy of scale in that the antenna need only be rotated throughout 360.degree. of the azimuth angle. The antenna of the '019 patent includes a plurality of waveguides disposed in parallel, wherein each waveguide has a plurality of slots disposed along the waveguide axis and having varying offset, length, and intersection angle values determined by a methodology. In addition, the reference discloses that the waveguide antenna array includes a feed waveguide for distributing electromagnetic waves to each of the plurality of waveguides which is disposed in a same plane as the array antenna and includes a first section extending along an end of each of the plurality of waveguides and a second section extending from a center of the antenna to a center of the first section which is perpendicular to the first section to thereby form a T-junction feed waveguide. The feed waveguide allows the antenna to be rotated in the horizontal or azimuth plane at a rotary center of the antenna without subjecting a converter that is coupled to an output of the antenna to any rotation. An asserted advantage of the '019 patent is that the converter can be kept in a stationary position thereby reducing the stress on the converter and prolonging the life of the converter.
Another issue with the various slotted waveguide antennas that have been proposed are the costs, the ease of manufacture, and the weight of the various waveguide antennas. For example, a conventional slotted waveguide antenna may be manufactured combining metal plates with a proper precision suitable for a desired frequency range to form a plurality of waveguides, and then securing the waveguides to each other in a transverse direction in an array-like manner. Subsequently, or in conjunction, depending upon the position of a feed waveguide, the feed waveguide may then be secured to the waveguide array. However, such a manufacturing process may not be suitable for mass production and therefore such a slotted waveguide antenna array may not be provided inexpensively using such a method. Moreover, such an embodiment of the slotted waveguide antenna may require reinforcement to avoid movement of the waveguides within the waveguide array. Further, such an embodiment of a waveguide may be typically made out of a metallic material with a high specific gravity which is, for example, for aluminum approximately 2.7 and yields a heavy slotted waveguide antenna array. Thus, conventional slotted waveguide antenna arrays are typically bulky, heavy and not suitable for efficient and cost effective mass production.
U.S. Pat. No. 4,916,458 discloses an embodiment of a slotted waveguide antenna that is intended to be manufactured easily, inexpensively and that includes a plurality of radiating waveguides each having at least one radiating slot. The antenna also includes a feed waveguide disposed at one end of each of the plurality of waveguides for feeding the plurality of radiating waveguides and a plurality of apertures between the feed waveguide and the radiating waveguides. The plurality of waveguides and the feed waveguide arc formed in a single plane by a dielectric plate that is sandwiched between conductive layers to form broad walls of the plurality of waveguides and the feed waveguide. In addition, either plated through-holes having a gap between each of the plated through-holes that is smaller than a wavelength of a signal propagating in the waveguides, or conductive pins having a similar gap therebetween and that are metalized on both sides, are inserted between the conductive layers and used to form the walls of the plurality of waveguides and the walls of the feed waveguide. In addition, the '458 patent discloses that outer peripheral walls of the plurality of waveguides and the feed waveguide can be provided by covering the dielectric plate material with a conductive material to form the outer peripheral walls. The slotted waveguide antenna of the '458 patent is asserted to be easy and inexpensive to manufacture and produce.
It is an object of the present invention to provide an improved leaky waveguide array antenna.